VISUALISATION USING GAME ENGINES Dieter Fritsch, Martin Kada Institute for Photogrammetry (ifp), University of Stuttgart, Germany Geschwister-Scholl-Strasse 24D, D-70174 Stuttgart [email protected] Commission V, WG 6 KEY WORDS: Visualisation, Virtual Reality, Real-Time, GIS, Modelling ABSTRACT: Geographic Information Systems (GIS) and Computer Aided Facility Management-Systems (CAFM) are currently undergoing the transition to storing and processing real 3D geospatial data. Applications for this type of data are, among others, location based services, navigation systems and the planning of large-scale construction projects. For presentation purposes and especially when working in the field, powerful visualisation systems are needed that are also capable of running on mobile devices like notebooks, personal digital assistants (PDA) or even cell phones. In such application areas, the free movement of the viewer’s position and the interaction with the data are of great importance. Real-time visualisation of 3D geospatial data is already well established and also commercially successful in the entertainment industry, namely in the market of 3D video games. The development of software in this field is very cost-intensive, so that the packages are often used for several game products and are therefore universally applicable to a certain extend. These so-called game engines include not only visualisation functionality, but also offer physics, sound, network, artificial intelligence and graphical user interfaces to handle user in- and output. As certain portions or sometimes even the whole engine are released as open source software, these engines can be extended to build more serious applications at very little costs. The paper shows how these game engines can be used to create interactive 3D applications that present texture-mapped geospatial data. The integration of 3D data into such systems is discussed. Functionality like thematic queries can be implemented by extending the internal data structures and by modification of the game’s accompanying dynamic link libraries. 1. INTRODUCTION applications. The rendering performance and quality continuously increases as the game industry develops and Since the time computer graphics has been introduced, the implements new visualisation technologies. And many of the demands for visualisation techniques have grown last generation engines or game-related libraries are now continuously. Today, the visualisation of three-dimensional available for little or even no cost in the form of open-source worlds seems to be a demanding task requested by many geo- software. The following sections will focus on both indoor related disciplines. This has led to Scientific Visualisation, and outdoor visualisation, will introduce some assorted game which is associated with solving visualisation problems of all engines and show prototypical applications that have been kind (McCormick, DeFanti and Brown, 1987). It offers built upon them (see e.g. Figure 1). Another aspect will be algorithms, software packages and advanced interactive tools (such as data gloves and other haptic interfaces) for graphics workstations, high end rendering machines and CAVE environments (see also Fritsch, 2003). Complementary are the developments in the computer game industry that has been developing game engines with amazing 3D computer graphics capabilities since the early 1990s. Due to the increasing interest in the consumer market, tremendous progress can be observed in the hardware and software. Game engines are powerful software packages that efficiently use rendering pipelines, special data-structures and speed-up techniques to visualise texture mapped 3D objects, scenes and 3D worlds in real-time (see e.g. Harrison, 2003). These software packages run nowadays on every commodity PC and 3D games already make their way on PDAs and even cell phones. The overall question is how to make best use of available technology to make the right application. Only few large projects use sophisticated hardware and software. For many 3D mapping applications, only commodity hardware and software is available. But even the Figure 1. Indoor visualisation showing a workspace at the daily user of computer graphics still aims at high quality Institute for Photogrammetry (ifp) rendered in visualisation at low costs. Game engines might be the missing real-time by the Quake 3 Arena game engine. part for realising visualisation software for geo-related the real visualisation of vegetation as this has been of special interest in game engines in the last years and big progress has been achieved. Coarse 3D Map Fine Geometric 3D Map Geometric Compilation Modelling Compilation 2. INDOOR VISUALISATION WITH Modelling GAME ENGINES Today, 3D computer games are highly complex systems that consist of a universal game engine and the specific game elements like the game rules and game data (e.g. geometry, Texture Texture Texture 3D Map textures and sound files). Main emphasis is put here in the Collection Processing Mapping game engine. This module is the heart of the computer game and represents the basic framework independent of the game. This general purpose feature allows the use of the engine for other applications, e.g. the indoor visualisation of building elements. Game engines incorporates all sorts of elements Figure 2. Workflow for generating 3D textured maps in that are vital to a game like physics, graphical user interface Quake III Arena (Beck, 2002). (GUI), artificial intelligence, network functionality, sound and event engine. Some game engines even contain scripting languages which makes it very easy to adapt the engines to computed (Abrash, 1997). The whole compilation process is one’s own needs. also depicted in Figure 3 (Beck 2002). The computer games Quake III Arena (developed by id A serious problem is, however, that existing datasets are Software) and Max Payne (developed by Remedy unlikely stored in a format that the game engine’s map Entertainment Ltd.) are action games, also called 3D Shooter compilers do understand or support. But fortunately, the or First Person Shooter. The player moves around in an ego- game tools are often available as source code so that the perspective and fights by means of several weapons within compilers can be modified to one’s own needs. the 3D world. This can be done either alone in single player mode or with multiple players in a network environment like e.g. a LAN or the internet. Both games have in common that Î the visualisation engine is what’s generally called an indoor BSP VIS Lighting engine. These engines are optimised by the use of specialised BRep indoor speed-up techniques like portal culling, a very popular Compilation technique first introduced by (Airey, Rohlf and Brooks Jr., Q3Radiant Editor Quake III Arena 1990). Based on the idea that walls are often large occluders, a viewer can only see into adjacent rooms through portals, which can be e.g. a door or a window. A potentially visible set (PVS) is pre-computed for all sets of viewpoints, a sort of Figure 3. Compilation process in Quake III that transforms database from which the rooms that are visible to the viewer a CSG model into a boundary representation and are identified. For densely occluded architectural scenes, the pre-computes a potential visibility set and light algorithm is able to cull away the better part of the scene. maps (Beck, 2002). Unfortunately, because the engines support very detailed environments, the virtual worlds are rather small and delimited. 2.2 Analysis Functionality and Interactivity 2.1 Data Acquisition and Integration The analysis of data is a very important aspect of GIS. Even though game engines do not offer a great variety of that kind The aforementioned game engines are of notable interest as of functionality, they at least feature some interesting both offer very good support for modifications. The game possibilities. By means of adding new entities to the Quake 3 related parts are available as source code and there exist free Arena engine, it is possible in the Q3Radiant editor to define editors for the creation of virtual 3D environment, which are new data that can be bound to every object in the map. (Beck, in the context of game engines usually called maps. These 2002) e.g. realises a thematic query in this way where the maps are modelled via Constructive Solid Geometry (CSG) objects are prompted by “shooting” at them. By removing the by logically combining simple forms like cuboids, pyramids weapons from the game, the result is a simple point and click and spheres. It is well-advised to create a coarse model before mechanism. The underlying object data, which is textual modelling the finer elements of the map. The resulting information about rooms and workspaces, is then displayed geometry can then be texture mapped with images that can on the screen (Figure 4). either be artificial or be generated from photographs. All Another engine element of great use is the path finding necessary steps are demonstrated in Figure 2 (Beck 2002). algorithm that is utilised by the artificial intelligence unit to Once the map is complete, it can not yet be used by the game control the non-player characters in the game. This engine, because the engine itself does not understand the data functionality can be turned into an indoor navigation system that comes from the editors. So the map must first be that guides the user through the virtual building. (Pfeiffer, compiled with designated tools that transform the CSG data 2002) implements a virtual museum guide that walks the into a boundary representation (B-Rep). In order to improve visitor through the exhibitions using the routing and trigger the performance of the scene rendering, the visibility functionality of the Max Payne game engine (see Figure 5). database is generated and the lighting and shading are pre- Figure 4. The result of a thematic query shows that this Figure 6. The Unreal Engine 2 is equally suited for indoor door leads to the room of the GIS group.